MAPKK CsSTE7 is critical for appressorium formation and pathogenicity in pepper anthracnose fungus, Colletotrichum scovillei

Colletotrichum scovillei, a member of the Colletotrichum acutatum species complex, causes severe anthracnose of pepper fruit, reducing yield and quality. However, the molecular mechanisms underlying its pathogenesis are unknown. Ste7 kinase in the Fus3/Kss1-related mitogen protein kinase signaling pathway plays an important role in plant infection by phytopathogenic fungi. In this study, the function of CsSTE7, an ortholog of Ste7, was investigated in C. scovillei using a targeted gene deletion mutant (ΔCsste7). Compared to the wild type, ΔCsste7 had normal mycelial growth, but conidial morphology, germination of conidia, and tolerance to cell wall integrity and osmotic stresses were defective. Importantly, ΔCsste7 was completely defective in appressorium formation and causing anthracnose on pepper fruits. These defects were restored in the complemented strain (Csste7c). The results suggest that CsSTE7 is essential for development and pathogenicity of C. scovillei.